Infection of the anogenital skin with human papillomavirus (HPV) results in exophytic or flat warts, and infection with some genotypes is also accepted as an antecedent cause of anogenital cancer. Current treatment modalities for genital warts are generally destructive and include surgery, cautery, laser surgery, and caustic chemicals as described in, for example, Beutner et al., 1997, Am. J. Med. 102 28-37. There is a high treatment failure and disease relapse rate, varying from 30-70%, after destructive treatment of exophytic warts which is discussed in Barrasso, R., 1998, J. Obstet. Gynecol. 18 S70-S71. Warts persist longer and return more frequently in immunosuppressed patients as referred to in Bouwes et al., 1997, Clin. Dermatol. 15 427-437, suggesting a role for the immune system in the resolution of the lesions. A role for local immunity is further supported by the partial therapeutic effectiveness of interferons as referred to in Frazer, I. H. & McMillan, N. A. in Clinical Applications of the Interferons (eds. Stuart-Harris, R. & Penny, R. W.) 79-91 (Chapman and Hall Medical, London, 1997), and of topical application of the immune enhancer Imiquimod which is discussed in Beutner et al., 1998, Antimicrob. Agents Chemother. 42 789-794. Immunoprophylaxis against HPV infection is proposed which is discussed in Hines et al., 1998, Curr. Opin. Infect. Dis. 11 57-61 and Hagensee, M. E., 1997, Infect. Med. 14 555-556, particularly because of the association of some papillomavirus (PV) genotypes with cancer. Expression of the PV capsid protein L1 or the L1 and L2 proteins in eukaryotic expression systems results in the assembly of this protein into papillomavirus virus-like particles (VLPs) described in Zhou et al., 1991, Virology 185 251-257; Kirnbauer et al., 1992, Proc. Natl. Acad. Sci. USA 89 12180-12184 and Rose et al., 1993, J. Virol. 67 1936-1944, which morphologically and immunologically resemble the native virus. Immunization with recombinant VLPs of the relevant type results in effective prophylaxis against challenge with bovine, canine and cottontail rabbit papillomavirus in vivo as referred to in Breitburd et al., 1995, J. Virol. 69 3959-3963, Kirnbauer et al., 1996, Virology 219 37-44 and Suzich et al., 1995, Proc. Natl. Acad. Sci. USA 92 11553-11557, and protection correlates with antibody titre and can be transferred with antibody (Brietburd et al, 1995, supra).
Reference may also be made to U.S. Pat. No. 5,437,951 which makes it clear that it is already known that the ability of PV VLPs to induce high titre neutralizing antiserum makes them suitable for prophylaxis against communicable papillomatosis. Examples of appropriate subjects provided in this reference are (i) bovine animals which are susceptible to papilloma warts, (ii) all humans for non-genital types of HPV infection and (iii) sexually active humans for genital types of HPV infection.
U.S. Pat. No. 5,437,951 also makes it clear that prophylactic vaccination can be useful for productive PV lesions which usually express L1 and L2 capsid proteins. Such lesions may occur in benign infections such as warts of laryngeal papillomatosis. This reference also establishes that protective immunity against both benign and malignant PV disease can be induced by administration of an effective amount of recombinant L1 capsid protein to an individual at risk for PV infections. A vaccine comprising the capsid protein can be directly administered either parentally or locally according to conventional immunization protocols.
Thus, U.S. Pat. No. 5,437,951 as well as the Kirnbauer et al., 1996, supra, Breitburd et al., 1995, supra and Suzich et al., 1995, supra references are representative of a large number of references that show that is well known that vaccines containing PV VLPs can be used for prophylaxis or prevention of infection of papilloma warts.
Reference may also be made to the Kirnbauer et al., 1996, supra wherein it was ascertained that immunization with vaccines containing BPV L1-L2 VLPs in Incomplete Freund's adjuvant to calves with established papillomas was not as efficient as the use of these vaccines for prophylaxis.
It is also noted in Greenstone et al., 1998, Proc. Natl. Acad. Sci. USA 95 1800-1805 that while PV VLPs are a promising prophylactic vaccine candidate to prevent HPV infections, they are unlikely to have therapeutic effects because the virion capsid proteins are not detected in the proliferating cells of infected epithelia or in cervical carcinomas. In this reference, it was also found that injection of chimeric HPV16L1/L2-HPV16 E7 VLPs into mice protected the mice from tumour challenge even in the absence of adjuvant. However, HPV16L1/L2 VLPs were not effective in this regard, a not unexpected result since the tumor was and E7 bearing tumor.
A similar result was found in Peng et al., 1998, Virology 240 140-157 wherein hybrid or chimeric VLPs formed from HPV L1 which also incorporated a single HPV16 E7 cytotoxic T lymphocyte (CTL) epitope and a single HIV gp 160 CTL epitope induced a strong CTL response upon immunization.
Reference may also be made to WO98/28003 which reports studies on development of a therapeutic vaccine to treat cotton tail rabbit papillomavirus infection. Their data supports the premise that E proteins are an essential component of an effective therapeutic vaccine.
This belief in the requirement for various E proteins to formulate a therapeutic PV vaccine has led to a clinical trial for a HPV6 genital wart therapeutic based on L2E7 absorbed onto Alhydrogel (Thomson et al., (1999) Phase 1 safety and antigenicity of TA-GW, a recombinant HPV5 L2E7 vaccine for the treatment of genital warts. Vaccine 17 40-49)
Interestingly, even though most vaccine trials have incorporated various adjuvants as a formulation component, their importance has not been determined. On this subject reference may be made to Shirmbeck et al., 1996, Intervirology 39 111-119 which also showed that injection of 100 ng to 1 μg of native hepatitis B virus surface antigen (HBsAg) VLPs without adjuvant efficiently primes MHC Class I restricted CTL responses and that this demonstrates that such VLPs may be immunogenic.
Unexpectedly, it has now been ascertained by the present inventors that treatment of existing PV infections, inclusive of genital warts, can be achieved by vaccines containing PV VLPs without any E proteins or adjuvant. This is doubly surprising especially in the light of the observations made in the Greenstone et al., 1998, supra and Kirnbauer et al., 1996, supra references above. The Kirnbauer et al., 1996, supra and Peng et al., 1998, supra also establish that while use of prophylactic PV vaccines without adjuvant may be effective, this conclusion may only apply to chimeric VLPs. While Schirmbeck et al., 1998, supra establishes that HBsAg VLPs without adjuvant may be immunogenic, a similar conclusion could not be applied to PV VLPs having regard to the other references described above.